In general, the present invention relates to a method and apparatus for the detection of lamp failures. More particularly, the present invention relates to a method and system for the non-destructive testing of the integrity of the internal atmosphere of an incandescent lamps.
Incandescent lamps are typically manufactured with an evacuated internal atmosphere or an inert gas atmosphere. In situations where a leak develops in the lamp vacuum or the internal components of the lamp become contaminated during or after the manufacture of a lamp, the internal atmosphere within the lamp will become contaminated. The presence of oxygen around the hot filament of an electrical lamp results in a reaction between the oxygen and the tungsten of the lamp. As a result, oxidation forms on the lamp filament and collects on the inside of the glass bulb.
This condition of oxidation within the internal atmosphere of a bulb is commonly referred to as lamp "white out" because of a white film which collects within the lamp. In some instances, such a violation of the internal atmosphere of the lamp may immediately render the lamp inoperative. More commonly, the lamp initially appears fully operative. However, the lamp has a significantly shorter life span compared to a "good bulb". In many instances, a lamp with a contaminated internal atmosphere can remain operative for thirty (30) seconds or more before the filament breaks, thereby rendering the lamp inoperative. When a lamp whites out, the internal resistance of the lamp increases, while the current through the bulb correspondingly decreases.
Various types of lamp failure indicating devices have heretofore been proposed and utilized. Most prior known devices are directed towards arrangements operative for identifying completely inoperative (also referred to as burned out) lamps or bulbs. For example, U.S. Pat. No. 2,548,991 to McNabb, U.S. Pat. No. 4,222,047 to Finnegan, U.S. Pat. No. 4,348,613 to Hormel et al., and U.S. Pat. No. 5,008,626 to Boyd, disclose various devices operative for identifying burned out electrical lamps.
Generally, prior known devices such as those shown and described in the aforementioned patents apply current through a circuit to a test bulb. Failure of the lamp to complete the circuit serves to activate various forms of lamp failure indicating mechanisms.
While prior art devices have generally proven to be commercially acceptable for identifying complete bulb failure, most are not adapted to anticipate premature failure. More particularly, most are not adapted to anticipate premature failure of lamps which are initially operative as a result of a violated internal atmosphere.
For lamp applications where testing subsequent to installation is advantageous, prior known devices are unable to satisfactorily identify lamps which are initially operative, but which will prematurely fail. Some exemplary lamp applications include, but are not limited to, automotive vehicle applications for head lamps, stop lamps, tail lamps and the like. Subsequent to installation, lamps utilized in such applications are inaccessible without time consuming removal of parts.
U.S. Pat. No. 5,202,636 to Powell discloses a method for detecting lamp white outs. The method of Powell monitors the change in light output over a period of time by utilizing a focusing lens to impinge light emitted from an electrical lamp upon a phototransistor. Electrical output from the phototransistor is compared to the voltage applied to the lamp, and lamps are rejected if their increase light output lags behind the increase in applied voltage by more than a predetermined value. Disadvantageously, the method of Powell requires free access to the lamp.
While Powell is designed to detect lamps which may be subject to premature failure due to white out, it is also attendant with its own limitations. In this regard, isolation and focusing of the light emitted from a lamp is necessarily required. In lamp applications, such as the exemplary automotive applications discussed above, it is advantageous to test lamps after installation since occasionally the lamps are accidentally cracked during installation. The method of Powell is unable to test a lamp while operatively installed in a fixture such as a head light, tail light, or the like.
While previously known devices have proven to be relatively commercially acceptable for a wide range of applications, each is attended with drawbacks and/or inherent limitations, some of which have been discussed above. Most significantly, none of the prior known devices and techniques is operative to satisfactorily anticipate premature lamp failure by monitoring the internal resistance of the lamp over a short period of time. In addition, many prior devices and techniques are complex, cost prohibitive, or both.
Accordingly, it is a principal object of the method and apparatus of the present invention to provide a cost effective apparatus for verifying the integrity of electric lamps by monitoring the internal resistance of the lamps over a short time interval.